Aiming at the smooth switching between grid-connected and islanded mode of microgrid

the smooth switching control strategy of the grid-connected grid based on virtual synchronous generator（VSG）is proposed

and the VSG is introduced into the SC energy storage unit of hybrid energy storage system（HESS）. A quasi-synchronization control strategy is designed based on VSG structure and the traditional phase pre-synchronized strategy is improved so to be able to eliminate the unfavorable effect due to the sign change of phase difference and to accelerate the pre-synchronized process. In view of the switching impact caused by the change of the control strategies of the main source converter in the case of switching between grid-connected and islanded mode

the parallel control structure of two control strategies sharing an inner current loop and the current reference values mutual tracking mechanism is adopted to keep the reference order of the current loop identical in the case of switching. The simulation results show that

in case of gridconnected/islanded switching

there is no impact on ac bus voltage

current and energy storage side and the effectiveness of the proposed control strategy is verified.